Introduction:​ The purpose of this study was to investigate the effects of Dynamic Impact Loading Exercise (DILE) on radial bone mineral density (BMD) in healthy premenopausal women and to determine the relations among the mechanical characteristics of loading and the bone adaptations.

Methods:​ Twenty-four women (25-45 yr.) completed DILE 36 cycles a day, 3 days a week for 6 months. The exercised arm was allocated randomly to either the dominant side or the non-dominant side with the contralateral side serving as the non-exercised control. Subjects were also randomly assigned into either the damped or the non-damped treatment arms in order to vary the mechanical loading characteristics of the activity program. Measurements, including anthropometries, physical activity levels, hand grip strength, radial BMD at distal third, ultradistal, and total distal 1/3 radius, upper extremity kinematics, and reaction forces were recorded at baseline and after 6 months.

Statistics:​ Reliability of reaction force and upper extremity kinematics were assessed by Intraclass Correlation Coefficients (ICCs). Repeated-measures ANOVA was conducted to assess changes in physical activity level and hand grip strength, as well as the exercise effects and damping effects on bone adaptations. The damping effects on reaction force characteristics and joint kinematics were examined by one-way ANOVA. One-tailed Pearson’s correlation analyses were used to investigate the relations between the reaction force characteristics including peak load, impact load, loading rate, and impulse and changes in BMD (ABM D).

Results:​ DILE demonstrated highly reproducible loading profiles and joint kinematics. The average adherence rate was 93.3% and no injuries were reported. Although there were no significant bone adaptations observed after 6 months, the correlations between ABM D and mechanical characteristics o f loading, particularly peak loads and impact loads, were statistically significant. The correlations between the reaction force characteristics and ABM D were higher in the non-damped group than those in the damped group.

Conclusion:​ DILE appears to be a valid and reliable upper extremity musculoskeletal loading model using humans, and results of correlation analyses parallel findings of previous bone adaptation models employing animals. Findings suggest that further research, investigating the associations between mechanical loading events and human bone health, is warranted.